Positive electrode for use in lithium cell and lithium cell using the same

ABSTRACT

A positive electrode for use in a lithium battery using water as a dispersion medium, not causing a problem of deteriorating the battery performance due to corrosion of a collector or the like and not forming unevenness on the coating surface, as well as a lithium battery using the positive electrode, the positive electrode used being formed from a positive electrode paste containing a positive electrode active material represented by the following formula (I), a binder ingredient comprising a water dispersible elastomer and a water soluble polymer as a viscosity improver, water as a dispersion medium and a dispersing agent: 
 
Li x MPO 4    (I) 
(in the general formula (I) above, M represents a metal atom containing at least one of metal atoms selected from the group consisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0&lt;x&lt;2).

BACKGROUND OF THE INVENTION

The present invention concerns a positive electrode for use in lithiumcell and a lithium cell using the same.

As electrode materials for lithium secondary cell, it is generally touse carbon compounds such as graphite for a negative electrode and acomposite oxide as an electrode active material for a positiveelectrode. Such positive and negative electrodes are manufactured, forexample, by slurryfying an electrode active material, a binder and aelectrically conducting agent such as conductive carbon used optionallyfor improving the electron conductivity with a dispersion medium toprepare a paste or a coating solution, coating the same to an electrodecollector by a coater and evaporating the dispersion medium.

An organic dispersion medium such as N-methyl-2-pyrrolidone has beenused as the dispersion medium for manufacturing the coating solution butit involves a problem of toxicity in the manufacturing premise, aproblem in view of safety, effects of the dispersion medium wastes onenvironments, a problem of processing cost, etc. In view of the above,it has been demanded to use water which reduces manufacturing cost anddoes not cause such problems.

In the manufacture of the negative electrode, use of water has beenenabled recently as a dispersion medium by using a synthetic rubberlatex type adhesive and a viscosity improver, and a manufacturing methodcapable of avoiding the problems described above has become popular.

On the other hand, in the manufacture of the positive electrode, whileLiCoO₂ has been widely used generally as the positive electrode activematerial, when water is used as the dispersion medium upon preparing apositive electrode by a positive electrode paste using LiCoO₂ as thepositive electrode active material, this results in a problem that LiOR,etc. are formed by reaction of lithium ion in the active material andwater to cause corrosion of a collector and deteriorate the cellperformance. Accordingly, it is still customary at present to use astyrene butadiene rubber or polyvinylidene fluoride (PVDF) for thebinder and a non-aqueous dispersion medium such asN-methyl-2-pyrrolidone for the dispersion medium.

For solving the problem such as corrosion of the collector and enablingthe use of water as the dispersion medium, JP-A No. 2000-294252describes a positive electrode formed by coating the surface of acollector with a protective film of an oxalate salt or a compound ofelements selected from silicon, chromiun, and phosphorus. Further, JP-ANo. 2003-157836 proposes to coat the surface of the positive electrodeactive material with a protective film having electroconductivity.

However, the positive electrodes described above are not stillsufficient in view of the cell performance and since they require a stepof covering the collector, etc., they involve a problem that they aredisadvantageous also in view of the cost.

On the other hand, the present inventors have noted on lithium phosphatematerials such as LiFePO₄ as the positive electrode active material useof lithium phosphate in the organic dispersion medium system as thepositive electrode active material is shown, for example, in JP-T No.2000-509193, JP-A Nos. 9-134724, 2004-55493, etc.

When the present inventors have attempted to manufacture of a positiveelectrode by using lithium phosphates such as LiFePO₄ in an aqueoussystem, it has been found that the problem of the corrosion for thecollector less occurs. However, it has been found that the positiveelectrode active material agglomerates upon preparing the paste, tendingto cause unevenness on the paste coated surface.

The present invention has been achieved in view of the above and itintends to provide a positive electrode for use in a lithium cellexcellent both in electric characteristics and physical properties and alithium cell using the same, by manufacture from an aqueous coatingsolution using safe water as a dispersion medium instead of organicdispersion media used so far thereby solving the problem of toxicity inthe manufacturing premise, the problem of safety, and the problem of theeffects of dispersion medium wastes on environments and the problem ofthe processing cost, as well as solving the problem of degradation ofthe cell performance caused by corrosion etc. of collectors and theproblem for the occurrence of unevenness on the coated surface,

SUMMARY OF THE INVENTION

In order to solve the foregoing subject, the positive electrode for usein the lithium cell according to the present invention is formed from apositive electrode paste containing a positive electrode active materialrepresented by the following formula (I), a binder ingredient comprisinga water dispersible elastomer and a water soluble polymer as a viscosityimprover, water as a dispersion medium, and a dispersing agent:Li_(x)MPO₄   (I)(in the general formula (I) above, M represents a metal atom containingat least one of metal atoms selected from the group consisting of Mn,Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0<x<2).

The “dispersion medium” used herein is a material for dispersing theconstituent ingredients of the positive electrode paste and it includesthose dissolving a portion of the constituent ingredients, that is,functioning also as a solvent.

A preferred example of the positive electrode active material includesLiFePO₄.

As the dispersing agent, one or more of materials selected from thegroup consisting of nonionic surfactants, polycarboxylic acid compounds,compounds having sulfonic acid groups, and compounds having vinylpyrrolidone structure can be used suitably.

The lithium secondary cell according to the invention has a positiveelectrode of the invention described above, a negative electrode usingan active material capable of intercalating/deintercalating metallithium or lithium ion, and an electrolyte layer.

In the invention, since a lithium phosphate compound such as LiFePO₄ isused as the positive electrode active material and a specified positiveelectrode material composition containing a dispersing agent is adopted,even in a case where water is used as a dispersion medium in thepositive electrode preparing step, corrosion of a collector less occursand the problem of degrading the cell performance can be overcomewithout covering the collector differently from the prior art, and theproblem for the occurrence of unevenness during paste coating can alsobe overcome. Further, the lithium phosphate compound is an activematerial capable of solving the problems in view of the resource, costand safety of existent electrode active materials, being inexpensive andhaving high safety. Accordingly, a positive electrode for use in alithium cell having high thermal stability as the cell characteristicsand also excellent in the rate characteristic and the cyclecharacteristic can be provided at a reduce cost.

That is, according to the invention, a lithium cell of high performancecan be provided, as well as an effect in view of the manufacture capableof using safe water instead of organic dispersion media having high riskand involving various problems in view of handling can be obtained andit is also advantageous in view of the raw material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a graph showing the result of a rate characteristic test at10.2 C, 1 C, 3 C, and 5 C for beaker cells of Example 1;

FIG. 1(b) is a graph showing the result of a rate characteristic test at0.2 C, 1 C, 3 C, and 5 C for beaker cells of Comparative Example 1;

FIG. 1(c) is a graph showing the result of a rate characteristic test at0.2 C, 1C, 3 C, and 5 C for beaker cells of Comparative Example 2;

FIG. 2(a) is a graph showing the result of a cycle characteristic testat IC charge/discharge for beaker cells of Example 1;

FIG. 2(b) is a graph showing the result of a cycle characteristic testat IC charge/discharge for beaker cells of Comparative Example 1; and

FIG. 2(c) is a graph showing the result of a cycle characteristic testat IC charge/discharge for beaker cells of Comparative Example 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

1. Positive Electrode

The positive electrode active material used as a positive electrode foruse in a lithium secondary cell according to the invention isrepresented by the following formula (I):Li_(x)MPO₄   (I)(in the general formula (I) above, M represents metal species containingat least one of metal atoms selected from the group consisting of Mn,Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo, and 0<x<2).Among them those containing Fe for M are preferred and LiFePO₄ isparticularly preferred.

Olivine type LiFePO₄ has a theoretical capacitance as high as 170 mAh/gand is inexpensive, and can greatly save the cell manufacturing cost.Further it also has excellent properties as the positive electrodematerial such as showing scarce toxicity to human bodies orenvironments, causing less oxygen deintercalation and having highthermal stability.

The starting material for the positive electrode active materialincludes, for example, Li salts such as LiOH, Li₂CO₃, CH₃COOLi, and LiClas the Li source, Fe salts such as FeC₂O₄, (CH₃COO)₂Fe, FeCl₂, and FeBr₂as the Fe source, Mn salts such as MnCl₂ as the Mn source, Ni salt suchas NiCl as the Ni source, and Co₃O₄ as the Co source.

Also in a case where M is other elements, metal salts for each of theelements can be used.

For the P source, H₃PO₄, (NH₄)₂HPO₄, NH₄H₂PO₄, etc. can be used.

The positive electrode active material can be obtained usually byblending the starting materials at an aimed molar ratio and sinteringthem at a high temperature.

While the grain size of the positive electrode active material is notparticularly limited, the average grain size of primary particles isusually about from 10 nm to 100 μm and 30 to 250 nm of grain size ispreferred and 60 to 200 nm grain size is more preferred in that theelectron conductivity is favorable.

While lithium phosphate compound may be used as it is, a positiveelectrode active material of low conductivity such as LiFePO₄ may becompensated for electron conductivity by coating the surface ofparticles with carbon. The coating amount of carbon is, preferably, 1part by weight or more and 20 parts by weight or less and, mostpreferably, 1 part by weight or more and 10 parts by weight or lessbased on 100 parts by weight of the positive electrode active material.

Examples of the elastomer usable in the invention include a copolymer ofacrylonitrile and butadiene (NBR), a copolymer of acrylonitrile andhydrogenated butadiene (HNBR), a copolymer of styrene ad butadiene(SBR), a copolymer of styrene and acrylonitrile (SAN), a terpolymer ofacrylonitrile, butadiene and styrene (ABS), a terpolymer of styrene,acrylonitrile and styrene (SAS), a terpolymer of styrene, isoprene andstyrene (SIS), a terpolymer of styrene, butadiene and styrene (SBS), aterpolymer of ethylene, propylene and diene (EPDM)), astyrene/ethylene/butene/styrene (SEES) polymer, a polyurethaneelastomer, polychloroprene (CR) or 2-chloro-1,3-butadiene,polyisobutylene (PIB), polyisoprene, polybutadiene, anethylene/propylene copolymer (EPR), a copolymer of ethylene and vinylacetate (EVA), a copolymer of ethylene and acrylate ester (EMA, EEA,etc.), a vinyl pyrrolidone/vinyl acetate copolymer, and mixturesthereof. The polymers may have a cross-linked structure.

Among the elastomers described above, the styrene butadiene copolymer(SBR) and an acrylonitrile butadiene copolymer (NBR) are preferred, SBERbeing particularly preferred.

As the water soluble polymer, one or more members selected fromcelluloses such as carboxymethyl cellulose (CMC), methyl cellulose,ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methylcellulose, and hydroxyethyl methyl cellulose; polycarboxylic acidcompounds such as polyacrylic acid, and sodium polyacrylate; compoundshaving a vinyl pyrrolidone structure such as polyvinyl pyrrolidone;polyacrylamide, polyethylene oxide, polyvinyl alcohol, sodium alginate,xanthane gum, carrageenan, guar gum, agar, and starch can be used, andamong them, carboxymethyl cellulose salt is preferred.

In a case where the water soluble polymer is a carboxymethyl cellulosesalt, the etherification degree thereof is preferably from 0.3 to 2.0,particularly preferably, from 0.45 to 1 in view of solubility to water,storage stability and manufacturing cost.

In a case of using the dispersible elastomer and the water solublepolymer are used for the positive electrode, the same combination can beapplied for the negative electrode to provide an advantage that the samematerial can be used for both electrodes.

As the water, distilled water, ion-exchanged water, and superpure waterare preferred, and the ionic conductivity thereof is preferably 0.5 mS/mor less, more preferably, 0.1 mS/m or less, and organic carbon is,preferably, 100 μg C/L or less, more preferably, 50 μg C/L or less, zincis, preferably, 0.5 μg Zn/L or less, more preferably, 0.1 μg C/L orless, silica is preferably 50 μg SiO₂/L or less, more preferably, 2.5 μgSiO₂/L or less, chloride ions are preferably, 10 μg Cl⁻/L or less, morepreferably, 1 μg Cl⁻/L, and sulfate ions are, preferably 10 μg SO₄ ⁻²/Lor less and, more preferably, 1 μg SO₄ ⁻²/L or less.

In the invention, use of the dispersing agent can prevent agglomerationof particles and makes the coating of the active material layer smoothupon manufacture of the positive electrode.

Examples of the dispersing agent include nonionic surfactants such aspolyoxyethylene tridecylether, polyoxyethylene branched decyl ether,polyoxyethylene isodecyl ether, polyoxyethylene lauryl ether,polyoxyalkylene lauryl ether, polyoxyethylene oleylether,polyoxyethylene alkyl ether, polyoxyethylene styrenated phenyl ether,polyoxyethylene castor oil, polyoxyethylene hardened castor oil,polyoxyethylene oleate ester, polyoxyethylene distearate ester,polyoxyethylene polyoxy propylene block polymer, sorbitan trioleate,sorbitan sesquioleate, sorbitan monooleate, sorbitan inonostearate,sorbitan mono coconut fatty acid ester, polyoxyethylene sorbitan monococonut fatty acid ester, polyoxyethylene sorbitan monostearate,polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitanmonooleate, polyoxyethylene lanolin alcohol ether, polyoxyethylenelanoline fatty acid ester, polyoxyethylene alkyl amine ether, coconutfatty acid diethanolamide, acetylene glycol, acetylene alcohol,acetylene glycol alkylene oxide adduct, acetylene alcohol alkylene oxideadduct; compounds having a sulfonic acid group such as aromatic sulfonicacid formalin condensation products such as sodium β-naphthalene sulfateformalin condensation products, special sodium aromatic sulfate formalincondensation products, sodium alkyl naphthalene sulfonate formalincondensation products, and sodium polystyrene sulfonate, and sodiumlignine sulfonate; polycarboxylic acid compounds such as ammoniumpolycarboxylate salts, sodium polycarboxylate salts, polyoxyethylenealkyl ether sulfate salts, polyacrylic acid, and sodium polyacrylate;compounds having a vinyl pyrrolidone structure such as polyvinylpyrolidone and a copolymer of vinyl pyrrolidone and acrylic acid; andanionic surfactants such as polyoxyethylene alkyl ether, and among them,the nonionic surfactants, polycarboxylic acid compounds, compoundshaving a sulfonic acid group and compounds having a vinyl pyrrolidonestructure are particularly preferred one or more dispersing agents maybe used in combination.

The blending ratio of the positive electrode active material, waterdispersible elastomer, water soluble polymer, dispersing agent andwater, as a ratio based on 100 parts by weight of the positive electrodeactive material (as solids) is as follows. The elastomer is, preferably,0.5 part by weight or more and 12 parts by weight or less, morepreferably, 1 part by weight or more and 6 parts by weight or less. Thewater soluble polymer, is preferably, 0.1 part by weight or more and 12parts by weight or less, more preferably, 0.5 part by weight or more and4 parts by weight or less. The dispersing agent is, preferably, 0.05part by weight or more and 10 parts by weight or less, more preferably,0.2 part by weight or more and 5 parts by weight or less. Water is,preferably, 20% by weight or more and 95% by weight or less, morepreferably, 40 parts by weight or more and 70% by weight or less in thepaste.

In order to enhance the dispersing effect, an organic dispersion mediumsuch as N-methyl-2-pyrrolidone, acetonitrile, methanol, ethanol, andisopropyl alcohol may be incorporated at the ratio of 20% by weight orless in the dispersion medium component within a range not departing thepurpose object of the invention.

As an ingredient other than those described above, an electricallyconducting agent may be added in order to enhance electroconductivity,and one or more carbonaceous materials such as carbon black, acetyleneblack and graphite which has been used so fat for the positive electrodecan be used.

The positive electrode of the invention is manufactured by preparing apaste-like positive electrode material by mixing each of the ingredientsdescribed above, coating the same to an aluminum foil or the like to bea collector and evaporating the dispersion medium. It is preferred thatthe elastomer is prepared into an emulsion, and the water solublepolymer is previously prepared into an aqueous solution of about from0.5 to 10%.

The method, the order, and the like of mixing each of the ingredientsdescribed above are not particularly limited, and for example, theactive material and the electrically conducting agent can be used whilebeing mixed previously. For the mixing in this case, a mortar, a millmixer, a ball mill such as a planetary ball mill or a shaker type ballmill, mechanotusion or the like can be used. Also the method for theaddition of the dispersing agent is also not particularly restricted,and it can be used as an aqueous solution at a concentration of 0.5% byweight or more or can be used as it is. In addition, the electricallyconducting agent can be used in a state of a liquid electrifyingdispersion in which the electrically conducting agent is previouslydispersed in an aqueous solution of the dispersing agent.

2. Lithium Secondary Battery

The lithium secondary battery of the invention is composed of thepositive electrode, the negative electrode and the electrolyte layer forthe lithium secondary battery of the invention.

The negative electrode is preferably capable ofintercalating/deintercalating metalic lithium or lithium ions, and thematerial constitution is not particularly limited but known materialscan be used.

As a specific example, a negative electrode prepared by coating amaterial obtained by mixing a negative electrode active material and abinder to a collector can be used.

As the negative active material, known active materials can be used withno particular restriction. For example, carbon materials such as naturalgraphite, artificial graphite, less graphitizing carbon, easilygraphitizing carbon, metal materials such as metallic or alloyedlithium, or tin compounds, lithium transition metal nitrides,crystalline metal oxides, amorphous metal oxides and electroconductivepolymers can be used.

As the binder, organic or inorganic binders can be used, and forexample, all of aqueous dispersible elastomers mentioned as those usablefor the positive electrode such as polyvinylidene fluoride and styrenebutadiene copolymers, and water soluble polymers as a viscosity improvercan be used.

As a collector for the negative electrode, for example, copper, nickeland the like fabricated in the form of a mesh, punched metal, expandedmetal or a planar shaped foil can be used.

The electrolyte layer is a layer put between the positive electrode andthe negative electrode, which is a layer containing an electrolytesolution or a polymer having an electrolyte salt dissolved therein or apolymeric gel electrolyte. In a case of using the electrolyte solutionor the polymeric gel electrolyte, it is preferred to use a separator incombination.

The electrolyte may be an electrolyte which is used in ordinary lithiumsecondary batteries, and comprises an electrolyte salt and a non-aqueousmedium.

The electrolytic salt includes, for example, LiPF₆, LiBF₄, LiClO₄,LiAsF₆, LiCl, LiBr, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiC(CF₃SO₂)₃, LiI, LiAlCl₄,NaClO₄, NaBF₄, NaI, and the like, and particularly includes inorganiclithium salts such as LiPF₆, LiBF₄, LiClO₄, LiAsF₆, and organic lithiumsalts represented by LiN(SO₂C_(x)F_(2x+1))(SO₂C_(y)F_(2y+1)), in which xand y each represents 0 or an integer of from 1 to 4, and x+y is from 2to 8.

The organic lithium salt includes, specifically, LiN(SO₂F)₂, LiN(SO₂CF₃)(SO₂C₂F₅) , LiN(SO₂CF₃)(SO₂C₃F₇), LiN(SO₂C₄F₃)(SO₂C₄F₉),LiN(SO₂C₂F₅)₂, LiN(SO₂C₂F₅)(SO₂C₃F₇), LiN(SO₂C₂F₅)(SO₂C₄F₉), etc.

Among them, LiPF₆, LiBF₄, LiN (CF₃SO₂)₂, LiN(SO₂F)₂, LiN(SO₂C₂F₅)₂, etc,are preferably used as the electrolyte since they are excellent inelectric characteristics.

One or more kinds of electrolyte salts may be used.

The organic solvent in which the electrolyte salt is dissolved is notparticularly restricted so long as it is an organic solvent to be usedfor a non-aqueous electrolyte solution of ordinary lithium secondarybatteries, and includes, for example, carbonate compounds, lactonecompounds, ether compounds, sulfolane compounds, dioxolane compounds,ketone compounds, nitrile compounds and halogenated hydrocarboncompounds. They specifically include carbonates such as dimethylcarbonate, methyl ethyl carbonate, diethylcarbonate, ethylene carbonate,propylene carbonate, ethylene glycol dimethylcarbonate, propylene glycoldimethyl carbonate, ethylene glycol diethyl carbonate, and vinylenecarbonate, lactones such as γ-butyrolactone, ethers such asdimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran,tetrahydropyran, and 1,4-dioxane, sulfolans such as sulfolane and3-methyl sulfolane, dioxolanes such as 1,3-dioxolane, ketones such as4-methyl-2-pentanone, nitrites such as acetonitrile, propionitrile,valeronitrile, benzonitrile, halogenated hydrocarbons such as1,2-dichloroethane, and other ionic liquids such as methyl formate,dimethyl formamide, diethyl tormamide, dimethyl sulfoxide, imidazoliumsalts, and quaternary ammonium. Further mixtures thereof may also beused.

Among the organic solvents described above, it is particularly preferredthat one or more kinds of non-aqueous media selected from carbonates arecontained since they provide excellent solubility, dielectric constantand viscosity of the electrolyte.

The polymeric compounds to be used for the polymeric electrolyte or thepolymeric gel electrolyte include, for example, polymers such as ofether, ester, siloxane, acrylonitrile, vinylidene fluoride,hexafluoropropylene, acrylate, methacrylate, styrene, vinyl acetate,vinyl chloride, and oxetane or polymeric materials having a copolymerstructure thereof or a cross-linked product thereof, and one or morepolymeric materials may be used. The polymeric structure is notparticularly restricted, and, polymeric materials having an etherstructure such as polyethylene oxide are particularly preferred.

The electrolyte is contained in a battery container, as a liquidelectrolyte in liquid-type batteries, as a precursor solution having apolymer dissolved in the liquid electrolyte in gel-type batteries, andas a polymer before cross-linking having an electrolyte salt dissolvedtherein in solid electrolyte-type batteries.

Also for the separator, separators used for ordinary lithium secondarybatteries can be used with no particular restriction, and for example,porous resins and non-woven fabrics made, for example, of polyethylene,polypropylene, polyolefin or polytetrafluoroethylene can be used.

Examples of the invention will be described below, but the invention isnot limited to the following examples.

EXAMPLE 1

100 g of LiFePO₄ with 5% by weight of a carbon coating amount as apositive electrode active material, 10 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 120 g of an aqueous 2 wt % solution of carboxynethyl cellulosewith an etherfying degree of from 0.45 to 0.55 (CELOGEN PL-15,manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosity improver, and0.5 g of a nonionic surfactant having a polyoxyethylene styrenatedphenyl ether structure (trade name of products: NOIGEN EA-137,manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agent weremixed by a homo-mixer for 30 min. 10 g of an aqueous 40 wt % solution ofthe SBR emulsion (trade name of products: MB-400B, manufactured byNippon Zeon Co.) as a binder and 50 g of water as a dispersion mediumwere added to the mixed solution, stirred by a homo-mixer for 15 minand, further, mixed by a ball mill for 6 hours, to prepare a positiveelectrode paste.

The positive electrode paste was coated to an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

For the thus prepared positive electrode, it was visually observedwhether agglomerates of 0.5 mm diameter or more were present or not inthe active material layer.

Further, a charge/discharge test was conducted by using the obtainedpositive electrode in a 2-electrode type beaker cell. Metallic lithiumwas used for the negative electrode, and an LiPF₆ solution (1 mol/L)with a solvent of ethylene carbonate (EC)/γ-butyrolactone (GBL)/ethylmethyl carbonate (EMC)=3/2/5 (by volume ratio) is used as anelectrolyte.

The test cell was charged/discharge for one cycle at 0.25 mAh/g, and thedischarge capacitance was defined as an effective capacitance. In thecycle test, the effective capacitance was defined as 1 C for identicalcell. Using the same cell, a test was conducted for 200 cycles under thecondition for charge discharge at 1 C, and the retention ratio of thedischarge capacitance at 200 cycle was determined based on the dischargecapacitance at the initial 1 C discharge in the cycle test as thestandard capacitance. The voltage was 4.0 V to 2.0 V and the temperaturewas at 20° C.

Table 1 shows the result of observation for the active material layer,the effective capacitance, and the capacitance retention ratio after 200cycles.

EXAMPLE 2

100 g of LiFePO₄ with 2% by weight of a carbon coating amount as apositive electrode active material, 6 g of acetylene black (manufacturedby Denki Kagaku Kogyo Co.) as an electrically conducting agent, 100 g ofan aqueous 2 wt % solution of carboxymethyl cellulose with etherfyingdegree from 0.6 to 0.7 (CELOGEN WS-C, trade name of products,manufactured by Daiichi Kogyo Seiyaku Co.) and 1 g of a nonionicsurfactant of a polyoxyethylene styrenated phenyl ether structure as adispersing agent (NOIGEN EA-187, trade name of products manufactured byDaiichi Kogyo Seiyaku Co.) were mixed by a homo-mixer for 30 min. 5 g ofa 40 wt % solution of an SBR einulsion (BM-400B, trade name of productsmanufactured by Nippon Zeon Co.) as a binder, and 50 g of water as adispersion medium were added to the mixed solution, stirred by ahomo-mixer for 15 min and, further mixed by a ball mill for 6 hours, toobtain a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode.

EXAMPLE 3

100 g of LiCoPO₄ with 5% by weight of a carbon coating amount as apositive electrode active material, 3 g of carbon black (trade name ofproducts: Ketchen Black EC, manufactured by AKZO NOBEL Co.) as anelectrically conducting agent, 100 g of an aqueous 1 wt % solution ofcarboxyrethyl cellulose with an etherfying degree of from 0.55 to 0.65(CELOGEN 3H, manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosityimprover, and 2 g of a sodium naphthalene sulfonate formalincondensation product (trade name of products: Lavelin FM-P, DaiuchiKogyo Seiyaku Co.) as a dispersing agent were mixed by a homo-mixer for30 min. 7.5 g of an aqueous 40 wt % solution of an SBR emulsion (tradename of products: BM-400B, manufactured by Nippon Zeon Co.) as a binderand 50 g of water as a dispersion medium were added to the mixedsolution, stirred by a homo-mixer for 15 min and, further, mixed by aball mill for 6 hours, to prepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and an LiBF₄ solution (2mol/L) with a solvent of ethylene carbonate (EC)/γ-butyrolactone(GBL)=3/7 (volume ratio) as an electrolyte.

EXAMPLE 4

100 g of LiFePO₄ with 3% by weight of a carbon coating amount as apositive electrode active material, 3 g of carbon black (trade name ofproducts: Kenchen Black EC, manufactured by AKZO NOBEL Co.) as anelectrically conducting agent, 90 g of an aqueous 1 wt % solution ofcarboxymethyl cellulose with an etherfying degree of from 1.15 to 1.45(CELOGEN HE-1500F, manufactured by Daiichi Kogyo Seiyaku Co.) as aviscosity improver, and 0.4 g of polycarboxylic acid (trade name ofproducts: POLITY 335S, manufactured by Lion Corp.) as a dispersing agentwere mixed by a homo-mixer for 30 min. 7.5 g of an aqueous 40 wt %solution of an acrylonitrile butadiene emulsion (trade name of products:BM-400B, manufactured by Nippon Zeon Co.) as a binder and 50 g of wateras a dispersion medium were added to the mixed solution, stirred by ahomo-mixer for 15 min and, further, mixed by a ball mill for 6 hours, toprepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution ofLiN(CF₃SO₂)₂ (0.5 mol/L) and LiN(SO2F)₂ (1 mol/L) with a solvent ofethylene carbonate (EC)/γ-butyrolacton (GBL)/propylene carbonate(PC)=2/2/6 (volume ratio) as an electrolyte.

EXAMPLE 5

100 g of LiFePO₄ as a positive electrode active material, 10 g ofacetylene black (manufactured by Denki Kagaku Kogyo Co.) as anelectrically conducting agent, 100 g of an aqueous 2 wt % solution ofhydroxypropyl methylcellulose as a viscosity improver, and 1 g of anon-ionic surfactant of a polyoxyethylene styrenated phenyletherstructure (trade name of products: NOIGEN EA-187 manufactured by DaiichiKogyo Seiyaku Co.) as a dispersing agent were mixed by a homo-mixer for30 min. 10 g of an aqueous 40 wt % solution of an SBR emulsion (tradename of products: BM-400B, manufactured by Nippon Zeon Co.) as a binderand 50 g of water as a dispersion medium were added to the mixedsolution, stirred by a homo-mixer for 15 min and, further, mixed by aball mill for 6 hours, to prepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution of LiPF₄ (1Mol/L) with a solvent of ethylene carbonate (EC)/γ-butyrolactone(GEL)/ethylmethyl carbonate (EMC) 3/3/4 (volume ratio) as anelectrolyte.

EXAMPLE 6

100 g of LiFe_(0.25)Ti_(0.75)PO₄ with 5% by weight of a carbon coatingamount as a positive electrode active material, 6 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 70 g of an aqueous 0.5 wt % solution of carboxymethyl cellulosewith an etherfying degree of from 0.65 to 0.75 (CELOGEN BSH-12,manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosity improver, and0.8 g of an anionic surfactant (trade name of products: Hitenol NE-05,manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agent weremixed by a homo-mixer for 30 min. 8 g of an aqueous 40 wt % solution ofan SBR emulsion (trade name of products: BM-400B, manufactured by Nipponzeon Co.) as a binder and 50 g of water as a dispersion medium wereadded to the mixed solution, stirred by a homo-mixer for 15 min and,further, mixed by a ball mill for 6 hours, to prepare a positiveelectrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution of LiBF₄ (1.5mol/L) with a solvent of ethylene carbonate (EC)/γ-butyrolacton(GBL)/dimethyl carbonate (DMC)=3/6/1 (volume ratio) as an electrolyte.

EXAMPLE 7

100 g of LiFePO₄ with 2% by weight of a carbon coating amount as apositive electrode active material, 6 g of acetylene black (manufacturedby Denki Kagaku Kogyo Co.) as an electrically conducting agent, 100 g ofan aqueous 2 wt % solution of carboxymethyl cellulose with an etherfyingdegree of from 0.6 to 0.7 (CELOGEN WS-C, manufactured by Daiichi KogyoSeiyaku Co.) as a viscosity improver, and 3 g of an aqueous 10% solutionof polyvinyl pyrrolidone (trade name of products: PITZCOL K-30,manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agent weremixed by a homo-mixer for 30 min. 10 g of an aqueous 40 wt % solution ofan SBR emulsion (trade name of products: BM-400B, manufactured by NipponZeon Co.) as a binder and 50 g of water as a dispersion medium wereadded to the mixed solution, stirred by a homo-mixer for 15 min and,further, mixed by a ball mill for 6 hours, to prepare a positiveelectrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution ofLiN(CF₃SO₂)₂ (1 mol/L) with a solvent of ethylene carbonate(EC)/γ-butyrolacton (GBL)/diethyl carbonate (DEC)=4/3/3 (volume ratio)as an electrolyte

EXAMPLE 8

100 g of LiFe_(0.5)Mn_(0.5)PO₄ with 2% by weight of a carbon coatingamount as a positive electrode active material, 6 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 100 g of an aqueous 2 wt % solution of carboxymethyl cellulosewith an etherfying degree of from 0.6 to 0.7 (CELOGEN WS-C, manufacturedby Daiichi Kogyo Seiyaku Co.) as a viscosity improver, and 1 g of anonionic surfactant having a polyoxyethylene styrenated phenol etherstructure (trade name of products: NOIGEN EA-187, manufactured byDaiichi Kogyo Seiyaku Co.) as a dispersing agent were mixed by ahomo-mixer for 30 min. 3 g of an aqueous 40% solution of an SBR emulsion(trade name of products: BM-400B, manufactured by Nippon zeon Co.) as abinder, 2g of a 40 wt % solution of an acrylic emulsion, and 50 g ofwater as a dispersion medium were added to the mixed solution, stirredby a homo-mixer for 15 min and, further, mixed by a ball mill for 6hours, to prepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution of LiPF₆ (1mol/L) with a solvent of ethylene carbonate (EC)/γ-butyrolacton(GBL)/ethyl methyl carbonate (EMC)=3/5/2 (volume ratio) as anelectrolyte.

EXAMPLE 9

100 g of LiFePO₄ with 2% by weight of a carbon coating amount as apositive electrode active material, 6 g of acetylene black (manufacturedby Denki Kagaku Kogyo Co.) as an electrically conducting agent, 100 g ofan aqueous 2 wt % solution of methyl cellulose (trade name of products:SM-400, manufactured by Shin-etsu Chemical Co.) as a viscosity improver,and 0.5 g of a nonionic surfactant (trade name of products: NOIGENEA-187, manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agentwere mixed by a homo-mixer for 30 min. 5 g of an aqueous 40% solution ofSBR emulsion (trade name of products: BM-400B, manufactured by Nipponzeon Co.) as a binder, and 50 g of water as a dispersion medium wereadded to the mixed solution, stirred by a homo-mixer for 15 min and,further, mixed by a ball mill for 6 hours, to prepare a positiveelectrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

A gel electrolyte was used for the electrolyte layer. For thepreparation of the gel electrolyte, tri-functional polyether acrylate(trade name of products. ELEXEL TA-140) manufactured by Daiichi KogyoSeiyaku Co.) as a polymer ingredient and a solution of LiBF₄ (2 mol/L)with a solvent of ethylene carbonate (EC)/γ-butyrolactone(GBL)/ethylmethyl carbonate (EMC)=3/6/l (volume ratio) as an electrolytesolution were used at 5:95(weight ratio) Further, 2000 ppm of an organicperoxide (trade name of products: PARKDOX 16 manufactured by KayakuAkuzo Corp.) was added as a heat polymerization initiator to obtain aprecursor solution. The precursor solution was poured into a beaker cellin which the positive electrode and the negative electrode werepreviously prepared, to conduct heat polymerization at 80° C. for 1 hourto obtain an electrolyte.

Evaluation was conducted in the same manner as in Example 1 except forusing the obtained positive electrode and the gel electrolyte.

EXAMPLE 10

100 g of LiFePO₄ with 2% by weight of a carbon coating amount as apositive electrode active material, 6 g of acetylene black (manufacturedby Denki Kagaku Kogyo Co.) as an electrically conducting agent, 100 g ofan aqueous 2 wt % solution of carboxyl methyl cellulose with anetherifying degree of from 0.6 to 0.7 (trade name of products: CELOGENWS-C, manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosityimprover, and 0.2 g of a nonionic surfactant having a polyoxyethylenestyrenated phenol ether structure (trade name of products: NOIGENEA-187, manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agentwere mixed by a homo-mixer for 30 min. 5 g of an aqueous 40% solution ofan SBR emulsion (trade name of products: BM-400B, manufactured by NipponZeon Co.) as a binder, and 50 g of water as a dispersion medium wereadded to the mixed solution, stirred by a homo-mixer for 15 min and,further, mixed by a ball mill for 6 hours, to prepare a positiveelectrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

100 g of graphite as a negative electrode active material, 2 g ofacetylene black as an electrically conducting agent, 100 g of an aqueous2 wt % solution of carboxymethyl cellulose (CELOGEN WS-C, trade name ofproducts, manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosityimprover were mixed by a homo-mixer for 30 min. 5 g of a 40 wt %solution of an SBR emulsion (BM-400B, trade name of productsmanufactured by Nippon Zeon Co.) as a binder, and 50 g of water as adispersion medium were added to the mixed solution, stirred by ahomo-mixer for 15 min and, further mixed by a ball mill for 16 hours, toobtain a negative electrode paste.

The negative electrode paste was coated on a copper foil as a collectorby an applicator and dried at 100° C. to obtain a negative electrode.

Tests were conducted in the same manner as in Example 1 except for usingthe thus obtained positive electrode, and the negative electrode, and asolution of LiB₄ (1.5 mol/L) with a solvent of ethylene carbonate(EC)/γ-butyrolacton (GBL)/ethyl methyl carbonate (EMC)=5/4/1 (volumeratio) as an electrolyte.

EXAMPLE 11

100 g of LiFe_(0.25)Mo_(0.75)PO₄ with 3% by weight of a carbon coatingamount as a positive electrode active material, 10 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 100 g of an aqueous 2 wt % solution of hydroxypropyl methylcellulose as a viscosity improver, and 1 g of a nonionic surfactanthaving a polyoxyethylene styrenated phenyl ether structure (trade nameof products: NOIGEN EA-187, manufactured by Daiichi Kogyo Seiyaku Co.)as a dispersing agent were mixed by a homo-mixer for 30 min. 10 g of anaqueous 40% solution of an SBR emulsion (trade name of products:BM-400B, manufactured by Nippon zeon Co.) as a binder, and 50 g of wateras a dispersion medium were added to the mixed solution, stirred by ahomo-mixer for 15 min and, further, mixed by a ball mill for 6 hours, toprepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution of LiBF₄ (1mol/L) with a solvent of ethylene carbonate (EC)/γ-butyrolactone(GBL)/ethyl methyl carbonate (EMC)=3/5/2 (volume ratio) as anelectrolyte.

EXAMPLE 12

100 g of LiFe_(0.3)Al_(0.7)PO₄ with 2% by weight of a carbon coatingamount as a positive electrode active material, 10 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 70 g of an aqueous 1 wt % solution of hydroxyethyl methylcellulose as a viscosity improver, and 1 g of a nonionic surfactanthaving a polyoxyethylene styrenated phenyl ether structure (trade nameof products: NOIGEN EA-187, manufactured by Daiichi Kogyo Seiyaku Co.)as a dispersing agent were mixed by a homo-mixer for 30 min. 8 g of anaqueous 40% solution of an SBR emulsion (trade name of products:BM-400B, manufactured by Nippon Zeon Co.) and 2 g of a 40 wt % vinylacetate emulsion as a binder, and 50 g of water as a dispersion mediumwere added to the mixed solution, stirred by a homo-mixer for 15 minand, further, mixed by a ball mill for 6 hours, to prepare a positiveelectrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution of LiBF₄ (1.5mol/L) with a solvent of ethylene carbonate (EC)/γ-butyrolactone(GBL)/ethyl methyl carbonate (EMC)w-3/6/1 (volume ratio) as anelectrolyte.

EXAMPLE 13

100 g of LiFePO₄ with 5% by weight of a carbon coating amount as apositive electrode active material, 10 g of acetylene black (trade nameof products: Denka Black, manufactured by Denki Kagaku Kogyo Co.) as anelectrically conducting agent, 100 g of an aqueous 2 wt % solution ofcarboxymethyl cellulose with an etherifying degree of from 0.6 to 0.7(CELOGEN WS-C, manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosityimprover, and 1 g of a nonionic surfactant having a polyoxyethylenestyrenated phenyl ether structure (trade name of products: NOIGENEA-187, manufactured by Daiichi Kogyo Seiyaku Co.) as a dispersing agentwere mixed by a homo-mixer for 30 min. 6.7 g of an aqueous 45% solutionof a nonionic urethane elastomer (trade name of products: Superflex 500,manufactured by Daiichi Kogyo Seiyaku Co.) as a binder, and 50 g ofwater as a dispersion medium were added to the mixed solution, stirredby a homo-mixer for 15 min and, further, mixed by a ball mill for 6hours, to prepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode, and a solution of LiPF₆ (1mol/L) with a solvent of ethylene carbonate (EC)/propylene carbonate(PC)/ethyl methyl carbonate (EMC)=2/1/7 (volume ratio) as anelectrolyte.

EXAMPLE 14

100 g of LiFe_(0.5)Mn_(0.5)PO₄ with 5% by weight of a carbon coatingamount as a positive electrode active material, 10 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 120 g of an aqueous 2 wt % solution of carboxymethyl cellulosewith an etherifying degree of from 0.45 to 0.55 (CELOGEN PL-15,manufactured by Daiichi Kogyo Seiyaku Co.) as a viscosity improver, and0.5 g of an acetylene alcoholic nonionic surfactant (trade name ofproducts: Olfin B, manufactured by Nisshin Kagaku Kogyo Co.) as adispersing agent were mixed by a homo-mixer for 30 min. 9.4 g of anaqueous 32% solution of an anionic urethane elastomer (trade name ofproducts: Superflex 420, manufactured by Daiichi Kogyo Seiyaku Co.) as abinder, and 50 g of water as a dispersion medium were added to the mixedsolution, stirred by a homo-mixer for 15 min and, further, mixed by aball mill for 6 hours, to prepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

Evaluation was conducted in the same manner as in Example 1 except forusing the thus obtained positive electrode.

COMPARATIVE EXAMPLE 1

100 g of LiFePO₄ with 5% by weight of a carbon coating amount as apositive electrode active material, 10 g of acetylene black(manufactured by Denki Kagaku Kogyo Co.) as an electrically conductingagent, 117 g of an aqueous 12 wt % solution of PVDF inN-methyl-2-pyrrolidone (trade name of products: #1120, manufactured byKureha Kagaku Co.), and 50 g of N-methyl-2-pyrrolidone as a dispersingagent were added to the mixed solution, stirred by a homo-mixer for 1hour, to prepare a positive electrode paste.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 140° C. to obtain a positiveelectrode.

A beaker cell was prepared by using the thus obtained positiveelectrode, the negative electrode and an electrolyte similar to those inExample 1, and a charge/discharge test was conducted.

COMPARATIVE EXAMPLE 2

100 g of LiCoO₂ (trade name of products: cellseed C5, manufactured byNippon Kagaku Kogyo Co.) as a positive electrode active material, 6 g ofacetylene black (manufactured by Denki Kagaku Kogyo Co.) as anelectrically conducting agent, 120 g of an aqueous 2 wt % solution of ancarboxymethyl cellulose (trade name of products: PL-15 manufactured byDaiichi Kogyo Seiyaku Co.) were mixed by a homo-mixer for 30 min. 5 g ofan aqueous 40 wt % solution of SBR emulsion (trade name of products:BM-400B, manufactured by Nippon Zeon Co.) as a binder and 50 g of wateras a dispersion medium were added to the mixed liquid, stirred by ahomo-mixer for 15 min, and further mixed by a ball mill for 6 hours toobtain a positive electrode.

The positive electrode paste was coated on an aluminum foil as acollector by an applicator and dried at 100° C. to obtain a positiveelectrode.

A beaker cell was prepared by using the thus obtained positive electrodeand the negative electrode and an electrolyte similar to those inExample 1, and a charge/discharge test was conducted. The test wasconducted within a range of the voltage from 4.2 V to 2.8 V.

For the beaker cells under the conditions in Example 1 and ComparativeExamples 1, 2, a rate characteristic test at 0.2 C, 1 C, 3 C, and 5 C,and a cycle characteristic test at 1 C charge/discharge were conducted.The results are shown in FIGS. 1(a)-1(c) and FIGS. 2(a)-2(c).

As can be seen from FIGS. 1(a)-1(c), for the battery using the positiveelectrode of the invention, a battery excellent in the bonding propertywith the collector by using a smaller amount of binder than the positiveelectrode using PVDF of Comparative Example 1 was obtained, and it wasexcellent in the characteristic at high rate (5 C). Further, since therate after 2 C was lowered abruptly in Comparative Example 2, it can beseen that preparation of a paste by using LiCoO₂ and using water as thedispersion medium is not preferred. Further, also in the cyclecharacteristic test, like in the rate characteristic, the cells ofComparative Examples 1, 2 caused lowering of capacitance not reachingthe 200 cycles. TABLE 1 Presence or Capacitance absence of Effectiveretention agglomerate capacitance ratio at No. particle (mAh/g) 200cycle (%) Example 1 none 160 99.6 Example 2 none 158 99.7 Example 3 none134 97.5 Example 4 none 138 98.0 Example 5 none 138 98.9 Example 6 none140 97.6 Example 7 none 144 99.5 Example 8 none 135 99.3 Example 9 none145 99.7 Example 10 none 140 99.5 Example 11 none 148 99.8 Example 12none 140 97.0 Example 13 none 160 99.5 Example 14 none 148 99.4Comparative Example 1 present 153 50 or less somewhat ComparativeExample 2 none 131 50 or less

1. A positive electrode formed from a positive electrode pastecomprising a positive electrode active material represented by thefollowing general formula (I), a binder ingredient comprising a waterdispersible elastomer and a water soluble polymer as a viscosityimprover, water as a dispersion medium and a dispersing agent:Li_(x)MPO₄   (I) (in the general formula (I) above, M represents a metalatom containing at least one of metal atoms selected from the groupconsisting of Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, Band Mo, and 0<x<2).
 2. A positive electrode according to claim 1,wherein the positive electrode active material is LiFePO₄.
 3. A positiveelectrode according to claim 1 or 2, wherein the dispersing agent is oneor more of materials selected from the group consisting of nonionicsufactants, polycarboxylic acid compounds, compounds having a sulfonicgroup, and compounds having a vinyl pyrrolidone structure.
 4. A lithiumsecondary battery having a positive electrode according to claim 1 or 2,a negative electrode using an active material capable ofintercalating/deintercalating metallic lithium or lithium ion, and anelectrolyte layer.